Adaptations to and Consequences of an Herbivorous Diet in Grouse and Waterfowl

I review diet selection in grouse and waterfowl in the context of their herbivorous diets and discuss adaptations to herbivory in these groups. Both grouse and waterfowl prefer plant foods containing higher concentrations of protein than nonpreferred foods; grouse and small waterfowl include invertebrates in the diet to meet protein demands during periods of high tissue production. Grouse tend to avoid plant foods containing high concentrations of anti-herbivore compounds and the relative roles of these compounds versus nutrients in diet selection by grouse is presently unclear. Grouse and waterfowl have similar digestive morphology, except for the ceca, which are 5 times longer in grouse than in geese. Enlarged ceca are associated with improved nitrogen economy in grouse; evolution of these structures in geese may have been precluded by energetic costs of carrying enlarged ceca during migration.